In, for example, an electric vehicle or a hybrid vehicle, a high-voltage battery is included as the drive power source of a motor. With such a high-voltage battery, a high voltage is obtained by connecting the plurality of cells of secondary cells (accumulators), for example, nickel-hydrogen cells or lithium cells in series.
Besides, all the secondary cells are charged or discharged by the same power. Therefore, in a case where the deteriorated states of the individual secondary cells are different, the secondary cells are liable to fall into overcharged states or overdischarged states. In this regard, the charged state of every unit cell needs to be confirmed lest the secondary cells should fall into the overcharged states or overdischarged states. For this purpose, a plurality of (for example, fifty-five) unit cells are divided into, for example, five blocks (namely, in order that one block may consist of eleven cells), and the voltage of each block is measured in real time by a voltage detecting IC which is disposed every block.
On this occasion, in the voltage detecting IC, the voltage of the unit cells (for example, eleven cells) of one block is measured. Further, a detected analog voltage signal is converted into a digital signal by an A/D converter which the voltage detecting IC includes, so as to transmit the digital signal to a main microcomputer. Thereafter, the abnormality of the secondary cells is decided by the main microcomputer, depending upon whether or not the value of the measured voltage lies within a predetermined range (refer to, for example, Patent Document 1).